A constant time controlled and/or a pH specific release of the active component of an orally administered drug is advantageous in medical treatment. The present invention relates to the oral administration of doses of metoprolol and its pharmaceutically acceptable salts such as, but not limited to, succinate, fumerate or benzoate of racemic metoprolol and the benzoate or sorbate of the S-enantiomer of metoprolol as disclosed in U.S. Pat. No. 4,957,745, U.S. Pat. No. 5,001,161 and U.S. Pat. No. 5,081,154 and incorporated herein by reference. The therapeutic effect of these drugs can be seen in the normalization of blood pressure for hypertension sufferers, and in the reduction of oxygen requirements in cardiac tissues, which induces beneficial affects on both angina pectoris and myocardial infarction.
Previously, inert cores for preparing controlled release forms of metoprolol pellets have been limited to water insoluble materials, because the use of water soluble materials combined with metoprolol created a great amount of osmotic pressure causing the controlled release pellets to burst and dump the drug. See U.S. Pat. No. 4,927,640 which is incorporated herein by reference.